<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <div class="progress" ref="progress"></div>
      <div class="progress-btn-wrapper" ref="progressBtn"
           @touchstart.prevent="progressTouchStart"
           @touchmove.prevent="progressTouchMove"
           @touchend="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>
</template>

<script>
import {prefixStyle} from 'common/js/dom'

const progressBtnWidth = 16
const trans = prefixStyle('transform')

export default {
  name: 'progress-bar',
  props: {
    percent: {
      type: Number,
      default: 0
    }
  },
  created () {
    this.touch = {}
  },
  methods: {
    progressTouchStart (e) {
      this.touch.initiated = true
      this.touch.startX = e.touches[0].pageX
      this.touch.left = this.$refs.progress.clientWidth
    },
    progressTouchMove (e) {
      if (!this.touch.initiated) {
        return
      }
      const deltaX = e.touches[0].pageX - this.touch.startX
      const offsetWidth = Math.max(0, this.touch.left + deltaX)
      this._offset(offsetWidth)
    },
    progressTouchEnd (e) {
      this.touch.initiated = false
      this._triggerPercent()
    },
    progressClick (e) {
      // this._offset(e.offsetX)
      const rect = this.$refs.progressBar.getBoundingClientRect()
      const offsetWidth = e.pageX - rect.left
      this._offset(offsetWidth)
      this._triggerPercent()
    },
    _offset (offsetWidth) {
      this.$refs.progress.style.width = `${offsetWidth}px`
      this.$refs.progressBtn.style[trans] = `translate3d(${offsetWidth}px,0,0)`
    },
    _triggerPercent () {
      const barWidth = this.$refs.progressBar.clientWidth
      const percent = this.$refs.progress.clientWidth / barWidth
      this.$emit('percentChange', percent)
    }
  },
  watch: {
    percent (newVal) {
      if (newVal >= 0 && !this.touch.initiated) {
        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
        const offsetWidth = newVal * barWidth
        this.$refs.progress.style.width = `${offsetWidth}px`
        this.$refs.progressBtn.style[trans] = `translate3d(${offsetWidth}px,0,0)`
      }
    }
  }
}
</script>

<style lang="less" scoped>
  @import '~common/css/variable';
  .progress-bar {
    height: 30px;
    .bar-inner {
      position: relative;
      top: 13px;
      height: 4px;
      background: rgba(0,0,0,0.3);
      .progress{
        position: absolute;
        height: 100%;
        background-color: @color-theme;
      }
      .progress-btn-wrapper {
        position: absolute;
        left: -8px;
        top: -13px;
        width: 30px;
        height: 30px;
        .progress-btn {
          position: relative;
          top: 7px;
          left: 7px;
          box-sizing: border-box;
          width: 16px;
          height: 16px;
          border: 3px solid @color-text;
          border-radius: 50%;
          background-color: @color-theme;
        }
      }
    }
  }
</style>
